Phosphate, or phosphorus, is the second most abundant mineral in the body with calcium being the most abundant. As a Phosphate salt with calcium, Phosphate is involved in the formation of bone and teeth. In other salt complexes, Phosphate is involved in acid-base balance. Phosphate is also important for the structures of DNA and cell membranes however, one of the most important roles of Phosphate is energy production in muscle as ATP and Phosphocreatine. Phosphate is also part of a compound in red blood cells known as 2, 3 DPG (2,3-diphosphoglycerate), which facilitates the release of oxygen to the muscle tissues.
Supplemental Phosphate salts have been shown to increase the concentration of 2,3 DPG in red blood cells, increasing VO2 max (a measure of aerobic fitness and a reduction in the production of lactate (Cade R, et al. Med Sci Sports Exerc. (1984) June; 16(3):263-8). Moreover, Phosphate has also been shown to enhance oxygen uptake and run performance without affecting the level of 2, 3 DPG (Kreider R B, et al. Med Sci Sports Exerc. (1990) April; 22(2):250-6). The metabolic rate can also be increased by Phosphate supplementation (Nazar K, et al. J Physiol Pharmacol. (1996) June; 47(2):373-83).
It has been noted that 86% of body's supply of phosphate is stored in the bone, 14% exists in the in the somatic cells and only 0.3% existing in the extracellular space. Therefore, with such small amounts of phosphate existing in the somatic cells and extracellular space the supply of phosphate in the body can be rapidly depleted during periods of strenuous muscle contraction or muscular loads.
Natural phosphate enhancement can be achieved through diet and supplement consumption. However, because the majority of phosphate within a body is stored in the bone an increase in phosphate, which is useful for cellular energetics through diet or direct supplementation alone, provides little if any increase in available phosphate to the somatic cells and extracellular space. Without an increase of the intracellular concentration of phosphate the energy required for muscle contraction will be quickly exhausted during physical activity. The energy requirements of contracting muscles involved in high-intensity exercise may increase 100-fold relative to resting muscles, exceeding the aerobic energy production capacity of the cells (Westerblad H, et al. News Physiol Sci. (2002) February; 17:17-21). In this case anaerobic metabolism will provide additional energy. However, high-intensity exercise results in an eventual reduced capacity for muscle contractile function, or fatigue. Thus, there is seemingly a link between anaerobic metabolism and fatigue.
In a 2000 review on the role of creatine in skeletal muscle, Casey and Greenhaff provide a thorough overview of energy supply and utilization in muscle (Casey A, et al. Am J Clin Nutr. (2000) August; 72(2 Suppl):607S-17S). Adenosine Triphosphate (ATP) is the direct energy source for contracting muscle as energy for muscle contraction is released from the dephosphorylation of ATP to yield Adenosine Diphosphate (ADP) and inorganic phosphate (HPO42− or PO43− or Pi) in the following reaction:ATP+H2O→ADP+Pi+H++energy  (reaction 1)
Therefore, the function of muscle is largely dependent on the availability of ATP. However, the concentration of ATP available in muscle at rest prior to the start of exercise is only enough to supply about 1-2 seconds of intense activity. ATP can be readily regenerated through the anaerobic dephosphorylation of available phosphocreatine. However, like ATP, the concentration of phosphocreatine in muscle is low and only enough to sustain muscle activity for about another 6 seconds. After repeated bouts of contraction, muscle phosphocreatine levels become nearly depleted (Greenhaff P L, et al. J. Physiol. (1993) January; 460:443-53). Fatigue, although likely multifaceted in terms of biochemical events, is the point at which the energy required by contracting muscle exceeds the level available either from the stored supply of ATP or the indirect synthesis of high-energy ATP through phosphocreatine dephosphorylation.
The enzyme Creatine Kinase (CK) catalyzes the following reaction to regenerate phosphocreatine:ATP+creatineADP+phosphocreatine+H+  (reaction 2)Reaction 2 is reversible depending on the energy state of the cell. In fast-twitch skeletal muscles, a large pool of phosphocreatine is available for immediate regeneration of ATP hydrolyzed during short periods of intense muscle contraction. Due to high CK activity in these muscles, the CK reaction remains in a near-equilibrium state, keeping the concentration of [ADP] and [ATP] almost constant over several seconds at the expense of phosphocreatine.
As can be noted from examination of reactions 1 and 2, a requirement of the regeneration of both ATP and phosphocreatine is a phosphate. Supplemental phosphate counters the chemically-induced reduction of ATP in rats (Rawson N E, et al. (1994) June; 266(6 Pt 2):R1792-6) and improves athletic performance in humans concomitant with increased cardiac function and aerobic capacity (Kreider R B, et al. Int J Sport Nutr. (1992) March; 2(1):20-47). Thus, ensuring adequate supply of intracellular, intercellular, extracellular and intra-tissue phosphate may decrease the reliance on anaerobic metabolism to regenerate ATP, thereby allowing ample regeneration of phosphocreatine stores, even during times of strenuous physical activity.
Therefore there is a need to supply the body with intracellular, intercellular, extracellular and intra-tissue supplemental amounts of phosphate to increase the availability of ATP and phosphocreatine, thereby aiding in periods when strenuous muscular contractions are desired.